The present invention relates to predicting radio wave propagation in a wireless communication environment. More specifically, the present invention relates to adaptively predicting radio wave propagation through a radio communication environment exhibiting heterogeneous propagation.
The planning and optimization of wireless communication networks results in the need for propagation models that accurately characterize the propagation of radio frequency signals in a given environment. Predictions of radio frequency signal, or radio wave, propagation are used to estimate quantities such as coverage, serving areas, interference, and so forth. These quantities, in turn, are used to arrive at equipment settings, for example, channel assignments, whose goal is to optimize capacity without sacrificing the quality of the network. Accordingly, it is highly desirable to employ a propagation model that is as accurate and reliable as possible, given the geographical data used as an input to the propagation model.
A conventional approach to propagation modeling is to employ a basic analytic model designed to determine the power received by a mobile station in terms of the power transmitted by a base station, the base station antenna gain, and the mobile station antenna gain. Once the transmitted power and the two antennas are selected, the propagation model reduces to evaluating the path loss of the radio frequency signal. Thus, it is highly desirable to compute the path loss as accurately as possible.
In general, path loss is the decrease, or attenuation, of the power of a signal usually occurring as a result of absorption, reflection, diffusion, scattering, diffraction, or dispersion, from an original level. In a wireless communication network, path loss may be determined from several components. For example, path loss may be a combination of distance dependent path loss, path loss due to terrain obstacles, path gain (or loss) due to sloping terrain, path gain caused by over-water propagation enhancement, path loss due to rain attenuation, and/or path loss due to street orientation relative to the propagation path.
There are several known models for predicting radio wave propagation. The selection of which propagation model to employ depends in large part on the land use and land cover (i.e., the propagation environment) because the particular propagation environment can affect the path loss of the radio wave. Some propagation environments include, for example, urban/suburban, rural agricultural, rangeland, forest land, water, wetland, barren land, tundra, perennial snow or ice, and so forth.
One conventional empirical propagation model typically used in radio engineering is a one slope approximation model, such as the known Okumura-Hata model. The one slope approximation model is an empirically-based formula for propagation loss derived from measured data obtained in Tokyo, Japan at particular frequencies. The Okumura-Hata model provides rapid calculation of path loss for line of sight conditions using terrain and land usage data. The Okumura-Hata model is applicable in a clutter-based propagation environment, such as urban/suburban or some rural propagation environments, in which the mobile station is located in the clutter.
Another technique for modeling radio wave propagation is the two slope approximation, also known as the two-ray model. In two-ray models, path loss at the receiver is predicted by considering only the contribution of a direct ray and a ground reflected ray of the radio frequency signal. Two-ray models are employed when the terrain is sufficiently smooth such that the terrain can be approximated by a flat-earth model. The two-ray model is applicable to flat-earth propagation environments, such as over water or barren land propagation environments.
Yet another technique for modeling radio wave propagation involves ray tracing. Ray tracing models attempt to model the propagation of radio frequency signals as rays radiating from the transmitter to the receiver. Ray tracing models are especially suited for predicting radio wave propagation in cluttered environments, such as in dense urban areas containing many tall buildings, in which a radio wave propagates along multiple propagation paths, i.e., multipaths.
Typically, network planning tools predict radio wave propagation by employing a single propagation model that predicts radio wave propagation throughout the entire wireless communication network. Alternatively, network planning tools may predict radio wave propagation by employing a single propagation model to predict radio wave propagation throughout a particular cell, or to predict radio wave propagation throughout a sector of a cell.
Unfortunately, if the propagation environment changes within the sector, a propagation model used for modeling radio wave propagation in that sector would no longer be an accurate predictor of radio wave propagation in that sector. Thus, what is needed is a method and system for making available to a network designer a propagation model suited to predicting radio wave propagation at a location within a sector.
Accordingly, it is an advantage of the present invention that a method and system are provided for predicting radio wave propagation.
It is another advantage of the present invention that the system and method predict radio wave propagation along radials emanating from a base station.
It is yet another advantage of the present invention that the system and method choose a particular propagation model for predicting radio wave propagation in response to a propagation environment at locations along the radials.
The above and other advantages of the present invention are carried out in one form by a computer-based method for predicting radio wave propagation along a radial emanating from a base station. The method calls for selecting one segment from a plurality of segments describing the radial and ascertaining a propagation environment through which the one segment traverses. The propagation environment is one of a first propagation environment and a second propagation environment. The method further calls for obtaining a switching parameter relative to the second propagation environment. A first propagation model is utilized to predict radio wave propagation at the one segment when the switching parameter fails to exceed a threshold, and a second propagation model is employed to predict the radio wave propagation at the one segment when the switching parameter exceeds the threshold.
The above and other advantages of the present invention are carried out in another form by a computing system for predicting radio wave propagation from a base station. The computing system includes a processor and a computer-readable storage medium. Executable code is recorded on the computer-readable storage medium for instructing the processor to perform operations including defining a plurality of radials emanating from the base station. The operations further include, for each of the radials, selecting one segment from a plurality of segments describing the radial, ascertaining a propagation environment through which the one segment traverses, the propagation environment being one of a clutter-based environment and a flat-earth environment, and obtaining a switching parameter relative to the flat-earth environment. The executable code further instructs the processor to perform operations including utilizing a clutter-based land propagation model to predict radio wave propagation at the one segment when the switching parameter fails to exceed a threshold, and to employ a flat-earth propagation model to predict radio wave propagation at the one segment when the switching parameter exceeds the threshold.
The above and other advantages of the present invention are carried out in yet another form by a computer-readable storage medium containing executable code for instructing a processor to choose one of a first propagation model and a second propagation model for predicting radio wave propagation along a radial emanating from a base station. The executable code instructs the processor to perform operations that include selecting one segment from a plurality of segments describing the radial and ascertaining a propagation environment through which the one segment traverses. The propagation environment is one of a first propagation environment and a second propagation environment. The executable code instructs the processor to perform further operations that include defining a threshold at which the second propagation environment exerts a greater influence on radio wave propagation than the first propagation environment, obtaining a switching parameter relative to the second propagation environment, choosing the first propagation model to predict radio wave propagation at the one segment when the switching parameter fails to exceed the threshold, and choosing the second propagation model to predict radio wave propagation at the one segment when the switching parameter exceeds the threshold.